Stainless steel treatment and product



Patented Dec. 23, 1941 STAINLESS STEEL TREATMENT AND PRODUCT Fredrick Kenneth Bloom, Baltimore, Md., as-

signor to Rustless Iron and Steel Corporation, Baltimore, Md., a corporation of Delaware No Drawing. Application December 26, 1939, Serial No. 311,014

Claims.

My invention relates to a process for treating stainless steel products, and more particularly to the treating of those products which can be hardened by heat treatment.

One of the objects of my invention is to provide a simple, practical and efficient method of producing stainless steel products to achieve a desired high elastic limit in combination with high ultimate strength and hardness.

Another object is to provide a process whereby hardenable stainless steel products may be given a high elastic limit in a direct and reliable manner without sacrifice to ductility.

A further object of my invention is to produce stainless steel products, such as rods and wire of high elastic limit, and to provide a simple method of achieving the same, which subsequently may be fabricated into articles of ultimate use without substantial loss of this'property.

Other objects in part will be obvious and in part will be pointed out hereinafter.

The invention accordingly consists in the combination ofsteps and the relation of each of thesame to One or more of the others as described herein, and in the resultant products or articles therefrom, the scope of the application of which is indicated in the following claims.

As conducive to a clearer understanding of certain features of my invention, it may be noted at this point that there are many applications in which it is desirable to have a corrosion re- Where hardening treatment is followed by a tempering or strain relieving'process, it is found that the elastic property of the steel is considerably improved. This tempering process consists of heating the metal to some temperature between 400 and 1100 F. and cooling. This operation follows the hardening treatment. The lowest possible tempering temperature is used in obtaining the mechanical properties desired,-

method of achieving, in the stainless steels of the hardenable types, a higher elastic limit than heretofore has been obtained, in combination with high-strength and hardness and without substantial loss in ductility.

Referring now more particularly to the practice of my invention, I find that excellent elastic properties of stainless steels are obtained by a particular combination of Working and heating treatments. I find that by slightly cold working sistant metal which is hard and also has the property of high elasticity. A high elastic limit is essential where the material must be able to bend under an appreciable stress without taking a permanent set, and must return to its original shape after the stress is removed. Examples of applications in which such properties are needed are automobile steering wheel spokes, pole type radio aerials, and the like.

Desired corrosion resistance in combination with strength and hardness is achieved to a fair degree in the hardenable stainless steels. These have a carbon content of about 0.08% to 0.50% and a chromium content of about 12% to 17%, with or without a nickel content of some 1.5 or 2%. Other ingredients, 'such as copper and molybdenum in small amounts, also may be present.

Heretofore, it has been the practice to harden such steels by heating them to 1750 to 1950 E, which is within their range of solid solution and then quenching. This operation gives a satisfactory hardness but for certain applications the resulting elastic limit is undesirably low.

the metal after a hardening operation and following this by a treatment of tempering, exceptional results are had. Only a small amount of cold work is necessary. Good results are had both where the cold work is by cold drawing and where it is by the alternate bending action of a straightening operation.

Hardenable stainless steels ordinarily are worked to a desired shape and size at the mill and hardened by quenching from a temperature above the carbide solution tempe'rature before shipment. According to a standard mill practice, this working is conducted at a temperature,

which usually is from about 1750 to 2050 F. In the practice of my invention,-the greatest part of all of the reduction through rolling, drawing,

etc., as usual may be done at this high temperature. quenched from this working temperature to give a desired hardness? This hardening treatment is the first step in my process of obtaining stainless steel products of high elastic limit.

The worked products conveniently are to an alternate bending operation. I find that ood results are obtained with either of these cold-working operations. In wire products, for example, a light reduction by cold drawing is what increased over that resulting from the old practices. I

While it is known that the physical properties of stainless steel, such as its ultimate strength,

eminently satisfactory. Excellent results like- 5 elastic limit and hardness, are improved through wise are had with only the mild form of cold a hardening treatment or through a cold-workworking had in the alternate bending operation. ing operation, these all usually increase in sub- In connection with the second step of my procstantially like amounts. In the cold-working ess, it is to be noted that the cold working can step of my invention, therefore, it reasonably be readily done on existing mill equipment withmight be expected that .a slight improvement in out incurring any expense other than that inthe physical properties would result. I find, volved in the ordinary rolling, drawing, straighthowever, as pointed out above, that where this ening and other processes. Extra working equipcold-working step is combined with a preceding ment therefore is unnecessary to the practice of hardening treatment and a succeeding tempermy invention. This, of course, is particularly mg treatment, there is a. phenomenal increase in important commercially since it permits the but one of these properties, namely the elastic practice of the process without additional worklimit. The others app to be afiected y s ing costs. might be expected. Although I am unable to ac- After cold working the metal, I carry out the count for this surprising phenomenon, it is an tempering treatment, representing the third step go observed fact as shown above. This unexpected in my process. This consists in heating the property of my process gives products such as metal to a temperature between 400 and 1100 rods and wire which are particularly adapted to F., preferably above 600 F. but below 930 F., applications where elasticity in combination with for about one hour. I find that the min P one or more of strength, ductility and corrosion of the Increase in dash}! 111111? is in the resistance, is important. Among these applicafirst ten P of temPFrmg Q tions are automobile steering wheel spokes and cases a desired increase in elastic limit 18 had automobile radio antennas Also, both in wire E ias g ggig fiz gfig gi ggi iggz gi and strip form, the material is useful in all manment has the special advantage of precluding i g gig and supports where elastlclty 15 any discoloration of the metal surface during I tempering. Following the tempering treatment, h fi' be fif z' thsre 1S ifi m the products are brought to room temperature my mven 1011 a 0 0 ing star ess s eel for packing and shipping or storing, as desired products to achieve a desired high elastic lmnt in To appreciate the advantages of my process, combination with strength, ductility and correferen e may be had to the f ll wing table, in rosion resistance, wherein the objects hereinbewhich there are presented the physical properties fore noted, together with y o ou y p acof th different types of t i l t l i wire tical advantages are successfully achieved. Moreform which have been subjected to different over, the process of my invention can readily be treatments. 40 carried out with eq pment already present in Processing method Ultimate El Rock- Analysis of stainless steel tensile EK ti r i ii i gig Type Procedure Strength 2 ness Lbaper. Lbaper.

sq.in. aq.m. Per cm Old treatment.. Hardened only 196,000 73,000 7.0 041 do Hardgned and tem- 193,000 100,000 7.0 041 El C 0.11%; Cr 12.55% New treatment. H rdenedmold-drawn 198,000 180,000 7.0 C 41 15% and tempered.

' do Herdened,straighten- 206,000 188,000 7.5 042 ed and tempered. Old treatment" Hardeeied and tem- 218,000 130,000 6.5 G0'38%; Cr13'49% New treatment- H denedmcld-drawn 230,000 220,000 5.5

5% and tempered. Old treatment" Hardened only 217,000 79,000 8.0 C45 do Hardened and tem- 219,500 130,000 a0 0-14 00.13%; Cr 14.70%; Ni 2.05% pered.

'New treatment. Hardened, straighten- 232,000 218,000 6.0 045 edend tempered.

From an inspection of the table given above, it will be seen that steel which has been subjected to my improved process suffers no decrease in hardness and very little, if any, decrease in ductility. The elastic limit of the metal is materially greater than that resulting from the standard processes of hardening or hardening and tempering. I find that the elastic limits of the stainless steel products of my invention amount to some 250% of those of like products which merely are hardened by heat treatment. As compared to stainless steel products which have been hardened and tempered, I find that my products have elastic limits amounting to some to of those products. Furthermills and in a simple manner entailing a minimum of additional expense.

As many possible embodiments may be made of my invention, and as many changes may be made in the embodiment herein set forth, it will be understood that all matter described herein is to be interpreted as being illustrative and not as being a limitation.-

.I' claim:

1. In treating stainless steel products which are hardenable by heat treatment and contain 12 per cent to 1'7 per cent chromium and .08 per cent to .50 per cent carbon, the art which comprises, quenching said products from a temperature between 1750" F. and 1950 F., cold-working the more, by my process the tensile strength is some- 76 same to an extent between a light finishing reduction to size and a reduction of 15 per cent, and then tempering said products at a temperature or from 400 F. to 1100 F.

2. In treating stainless steel products which are hardenable by heat treatment and contain 12 per cent to 1'7 per cent chromium and .08 per cent-to .50 per cent carbon, the art which comprises, first hardening said products, then giving the same a cold reduction of about 5 per cent, and then tempering the same at about 930 F.

a. In treating stainless steel wire which is hardenable by heat treatment and contain 12 per cent to 1'? per cent chromium and .08 per cent to .50 per cent carbon, the art which comprises, quenching the wire from a temperature of 1750 to 1950 F., then subjecting the wire to a cold-working operation as by the alternate bending of a straightening operation or a light cold-drawing which should not exceed a reduction. of 15 per cent, and thereafter heating the wire to a tem- V perature of 400 F. to 1100 F., and subsequently cooling the same to room temperature.

4. In treating stainless steels which are hardenable by heat treatment having a content of-0,08 per cent to 0.50 per cent carbon, 12 per cent to 1'7 per cent chromium, the art which comprises,

hardening the metal, cold working the same by a light finishing operation, and then tempering the metal at a temperature between 600 F. and 930 F.

5. In manufactures of the class described, hardened stainless steel wire including aboutQOB per cent to .50 per cent carbon and 12 per cent to 17 per cent chromium, subjected to the cold work of a straightening operation and tempered to achieve high elastic-strength in combination with desired hardness and ductility.

I FREDRICK KENNETH BLOOM. 

